This invention relates to selective reception of a radio signal with battery saving by a cellular mobile radio receiver movable in a plurality of cells assigned with radio signals of a plurality of signal formats. More particularly, this invention relates to a selective call radio receiving method and to a selectively called radio receiver of a received radio signal with automatic selection of one of the signal formats and in response to a selective call signal indicative of the radio receiver as a destination among a plurality of similar radio receivers which may present alive in the cells.
Such cellular selectively called radio receivers are widely used at present as mobile communication terminals, portable telephone handsets, and the like. For use by a great number of users, more and more higher bit rates have come into use. Moreover, various signal formats are in use.
A typical example of the signal formats is known as the POCSAG standard, which is specified in Autumn 1980 by the Post Office Code Standardisation Advisory Group (POCSAG) of London, the United Kingdom, as "Standard Message Formats for Digital Radio Paging". In connection with the POCSAG standard, a selectively called ratio receiver was invented by Motoki IDE, assignor to the present assignee, and was issued as U.S. Pat. No. 5,487,090. The specification of this Ide patent will be incorporated herein by reference.
A conventional selectively called ratio receiver is for operation in one signal format alone. In addition, the selectively called ratio receiver is operable at only one predetermined bit rate. It has consequently been impossible to use the conventional selectively called ratio receiver in a plurality of cells assigned with various signal formats and various bit rates even when the received radio signal of either another of the various signal formats or another of the various bit rates may have in one of the cells a good received state, such as no topographic disturbance, while the received radio signal of ones of the various signal formats and bit rates have an objectionable received state.
An improved selectively called radio receiver is disclosed in Japanese Patent Prepublication (A) No. 93,221 of 1989. This improved radio receiver is operable while carried across a plurality of cells in which radio signals of different radio frequencies are used with the radio signal of each radio frequency given a selected one alone of the various signal formats and a selected one alone of the various bit rates. The improved radio receiver comprises a state judging device for judging whether or not the received state is good in connection with a particular one of the radio frequencies that is used in one of the cells where a user has been attending to the radio receiver. It is possible to evaluate the received state by watching an electric field intensity, a bit error rate, and a state of synchronism between the radio signal and operation of the radio receiver.
If the received state is objectionable, the user might have moved from a first cell of the cells for the radio signal of a first radio frequency with a first signal format and a first bit rate to a second cell where the radio signal is given a second radio frequency with a second signal format and a second bit rate. In this event, the user manually deals with a switch of the improved selectively called ratio receiver to change the first radio frequency to the second radio frequency and thus from the first signal format and the first bit rate to the second signal format and bit rate. Alternatively, the improved selectively called radio receiver is automatically put into operation of searching among the different radio frequencies for the second radio frequency that gives a favorite received state of the received radio signal. The first signal format and the first bit rate are thereby switched to the second ones.
This radio receiver is excellently operable under the circumstances. The radio receiver is, however, insufficient for use in cells where radio signals of various radio frequencies are in use with the radio signal of each radio frequency used with a plurality of signal formats and a plurality of bit rates. That is, such a selectively called radio receiver is incapable of receiving in each cell a radio signal with a better received state than a radio signal which is currently received with a certain signal format and a certain bit rate.